Patrick Byrne's resignation Thursday came after the company issued a bizarre statement last week in which the former CEO referred to the "Deep State," called federal agents "Men in Black" and confirmed a journalist's stories detailing his relationship with Maria Butina, a gun-rights activist who was sentenced to prison for being an unregistered agent of Russia.
Overstock.com's shares fell 36 percent in the two days after the statement was made public.
Byrne, who founded the online discount retailer 20 years ago, said Thursday that he was "in the sad position" of having to step down.
"Though patriotic Americans are writing me in support, my presence may affect and complicate all manner of business relationships, from insurability to strategic discussions regarding our retail business," he said.
Overstock.com, based in Midvale, Utah, named company veteran and board member Jonathan E. Johnson III as interim CEO.
The company's shares jumped $1.62, or 8.3 percent, to close Thursday at $21.12.
In his statement last week, Byrne said he had helped law enforcement on three occasions, the last being "less about law enforcement and more about political espionage conducted against Hillary Clinton and Donald Trump (and to a lesser degree, Marco Rubio and Ted Cruz)." -- The Associated Press